Mikimoto Ginza 2

This commercial building in Tokyo’s Ginza district has been designed for Mikimoto, a company world famous for its pearl jewelry. This is a rectangular building, 17m wide by 14m deep, with nine stories above ground and one basement level. The lower levels are used as a shop and offices for Mikimoto and the upper levels are leased as offices.
“Mikimoto Ginza 2” is wrapped in four thin walls to create a tube structural system. There are no internal columns, and the floor slabs are a stack of nine homogeneous layers.

In previous projects we have integrated the structure and surface layers to express a strong presence, but with this project we used a steel plate-sandwitched concrete structure in which concrete is poured into a space between two steel plates. Panels composed of steel plates (t=6-12mm) sandwiched together with studs and structural reinforcements are made in a factory and conveyed to the construction site. After erection and adjustment on the site, they are welded together and 200mm of concrete is poured inside. Through this system, which treats the steel plates as expendable formwork, it was possible to create an extremely thin structure and achieve high strength and redundancy. Also, since it is a non-directional planar structural system, it was possible for openings to be inserted freely.

The openings of this building employ random shapes derived from a quasi-crystalline geometry generated by the dividing the façade planes with seven triangle shapes. By integrating the structure and the fluid opening pattern (as if capturing a moment of fluctuation), and through the use of a special coating, the building expresses both soft lightness and refined intensity. This design is not based on pure geometry, nor does it follow a (structural) expressionist approach, but employs a new method. It goes without saying that such a design has become possible for the first time through the use of structural analysis technology known as the “finite element analysis method”.

In order to realize flat facades without joints, the welded joints were smoothed flat on site and the steel received many layers of paint, from rust proofing to topcoats. By eliminating the joints usually found in curtain walls, the external image of the building presents a different kind of abstractness, and the multilayer coatings draw out the materiality of the steel plate to the maximum and directly express the strength of the structure.

Since we were challenging something very new, this project required sophisticated construction technology and verification by careful inspection. We made mock-ups, testing construction methods and evaluating performance through a trial and error process. The building was completed in December 2005, and has since become a focal point of architecture in the Ginza shopping area.

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14 photos and 7 drawings

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